In the wake of the biggest-ever document leak, pressure has been put on world leaders about their dealings in foreign trusts.

It's already claimed the scalp of Iceland's Prime Minister Sigmundur Gunnlaugsson, who resigned after public outrage over his storing of family money in offshore accounts.

The pressure has also been put on Mr Cameron after it was revealed he profited from selling his stake in his late father's Panama-based trust months before he became Prime Minister.

He's now pushing through a tax reform bill, and has released a summary of his tax returns from between 2009 and 2015.

Mr Little says he's in the process of pulling together his tax records dating back to around 2010. He says Mr Key should consider doing the same.

"John Key comes out of the finance sector, and for a lot of people at the senior levels -- at Merilll Lynch or whatever -- it's pretty routine for them to take tax minimisation steps, it would be unsurprising if he did that.

"He is the Prime Minister now and he is dealing with the issue of tax and the morality of tax-dodging. I think given all that, to give New Zealanders an assurance that he is squeaky clean and above board, he should be disclosing his tax records."

But Mr Key doesn't see the point in doing so, saying he's always complied with the standing orders committee, which sets out what disclosure it requires for MPs.

"It'd have to be a pretty big step to move in that regard. It wouldn't solve the issues people would want. They'd ultimately want all sorts of other disclosures around trusts and other things and you could start moving into spouses.

"We have a pecuniary interest list, we follow that carefully.

"This is just a stunt by Andrew Little. All he's trying to do is link me somehow to Panama which is not true, and everyone knows that's not true. They hacked those files a year ago, they looked through every politician and my name isn't on the list."

Mr Key says he doesn't have any offshore trusts, but does have two others in New Zealand -- the JP & BI Key Family Trust and the Aldgate Trust. The latter is a blind trust in which he is neither a trustee nor a beneficiary, while the other he is a beneficiary of.